1. Technical Field
The present invention relates to a semiconductor device and a boost circuit, particularly to the ones suitable for configuration of a charge pump circuit with a fully depleted silicon-on-insulator (hereafter “SOI”) transistor.
2. Related Art
In common semiconductor devices, field-effect transistors are formed on SOI substrates. This is because these transistors are latch-up free and are easy to isolate devices therein, and have a comparatively small source/drain junction capacitance. Particularly, since fully depleted SOI transistors allow rapid, lower power-consumption operations, researches for achieving the operation of the SOI transistors in a fully depleted mode are very active.
As semiconductor manufacturing processes advance, semiconductor integrated circuits become more multifunctional and highly integrated in a higher density, while the source voltage inside those semiconductor integrated circuits become lower and lower. Various power sources, including high voltage sources, are more often built in, as semiconductor integrated circuits become more multifunctional. For instance, 10V and/or more of high voltage is required for nonvolatile memories such as flash memory and electrically erasable programmable read-only memory (hereafter “EEPROM”), and for driver integrated circuits (hereafter “IC”) for display devices. In order to generate such high voltages with a boost circuit, a charge pump approach with which building-in the boost circuit to the semiconductor circuit is easy, is employed, instead of a switching regulator approach using coils and the like. Among the charge pump approach, Dickson charge pump circuit is commonly used, as disclosed in JP-A-2004-328901.
However, in common charge pump circuits, ground contact of substrate terminals of transistors needs to be provided in order to deal with the latch-up phenomenon. This involved a problem of conversion efficiency deterioration, since transistors that configure the charge pumps need to be high voltage proof, which increases an internal impedance of charge pump circuits.